This invention relates generally to a miniature motor used for audio equipment, precision instruments, automotive electrical equipment, etc., and more particularly to a miniature motor having an electrical noise preventing element and/or an over-current preventing element, and to a miniature motor in which the number of types of component members is reduced.
FIG. 1 is a longitudinal sectional front view illustrating the essential part of a miniature motor of a conventional type. In FIG. 1, numeral 1 refers to a case made of a metallic material, such as mild steel, formed into a bottomed hollow tubular shape, and having a permanent magnet 2 formed into an arc-segment shape, for example, and fixedly fitted to the inner circumferential surface of the case 1. To the case 1 fitted is a rotor comprising an armature iron core 3 facing the permanent magnet 2 and a commutator 4. Next, numeral 6 refers to a case cap made of an insulating material, such as a resin material, and fitted to an open end of the case 1. Numeral 45 refers to a brush formed into a rectangular shape in cross section, for example, and slidably fitted in a brush holder 15 provided on the inner end face of the case cap 6 in such a manner as to make sliding contact with the commutator 4.
Numeral 13 refers to a spring for forcing the brush 45 onto the commutator 4. Numeral 8 refers to an input terminal fixedly fitted after passed through the case cap 6, and electrically connected to the brush 45 via a pig-tail wire 14 on the inner end face of the case cap 6. Numerals 9 and 10 refer to bearings fixedly fitted to the bottom of the case 1 and the central part of the case cap 6, respectively, to rotatably support shafts 11 and 12 constituting the rotor 5.
With the aforementioned construction, when electric current is fed to the windings of the armature iron core 3 from the input terminals 8 and 8 via the pig-tail wires 14 and 14, the brushes 45 and 45, and the commutator 4 constituting the rotor 5, rotating force is imparted to the rotor 5 placed in a magnetic field formed by the permanent magnet 2 fixedly fitted to the inner circumferential surface of the case 1, causing the rotor 5 to rotate, thereby driving external equipment (not shown) via the shaft 11 on the output side.
In this type of miniature motor, means for preventing electrical noise by connecting a capacitor across the input terminals 8 and 8 is known. With this means, the capacitor is usually provided on the outer end face of the case cap 6 by connecting the lead wire of the capacitor across the input terminals 8 and 8 directly or via any other electrically conductive members by soldering, for example.
With a miniature motor in which a capacitor as an electrical noise preventing element is mounted on the outer end face of the case cap 6, an additional space for preventing interference with other components must be provided inside a system or equipment that uses the miniature motor as a drive unit. This construction of miniature motor therefore has a problem of impairing the miniaturization of a system or equipment in which the miniature motor is incorporated. If a choke coil, for example, is used as an electrical noise preventing element, together with the capacitor, the above problem could be further aggravated.
The above problem can be solved if the electrical noise preventing element is provided on the inner end face of the case cap 6. However, when additional electrical noise preventing elements are to be provided, the existence of a pair of brushes 45 on the inner end face of the case cap 6 makes it difficult and complicated to install lead wires for each element and the pigtail wires 14 for feeding power to the brushes 45. Furthermore, the lead wires and the pig-tail wires 14 tend to be entangled and shortcircuited.
If a special mounting member or electrically conductive member is used to facilitate the connection of these wires in a miniature motor of a construction in which a pair of input terminals 8 and 8 are not point-symmetric with respect to the motor axis, the mounting member or the electrically conductive member of different shapes and dimensions may have to be used for the positive and negative sides thereof, making it impossible to use common components. It also makes mounting operation and parts difficult to manage.